1. Field of the Invention
The present invention relates to a remote control of electric energy consumers, and more specifically is concerned with an apparatus for switching electric circuits.
The invention can be used in apparatus for exerting control over a plurality of electric energy consumers, for instance, group of electric motors in various industries, and in particular in coal mines.
2. Prior Art
There are known apparatus to exercise control over a group of electric motors (control station), which comprise a great number of contacts, intermediate relays and other switching elements, the number of which is determined by the number of remoutly controlled electric motors. These apparatus, however, are complex, bulky and feature a low service reliability.
Special problems are encountered in designing apparatus for controlling machines operating in mines in an explosive atmosphere. In this case in order to provide for safety operation a number of special requirements must be met, such as, for example, check of insulation of an electric circuit connecting the machine with an electric energy source.
To meet these requirements each set of apparatus designed for controlling an individual electric energy consumer is provided with a special control device.
USSR Author's Certificate No. 320,846 discloses an apparatus for switching high voltage equipment, which comprises a stationary contact panel having contacts located in a circle, an electromagnetic drive having an actuator mounted for rotation about and reciprocating motion along an axis passing through the centre of said circle and perpendicular to the plane of the contacts. The apparatus further includes a switching unit rigidly connected to the actuator of the electromagnetic drive and adapted to close and open contacts when the electromagnetic drive operates. Mounted on the electromagnet armature, which serves an an actuator, is a master cam constructed in the form of a coupling and having on its cylindrical surface a saw-like slot with a varying depth, intended for a pin to move therein, which pin is secured on the electromagnet frame.
When a voltage pulse is applied to the electromagnet coil the armature is pulled in response to which the pin moves along the surface of the saw-like slot to interact therewith and to thereby rotate the armature together with the switching element through an angle which is determined by a tooth spacing of the saw-like slot.
The above apparatus permits electric circuits to be switched only in succession and therefore does not allow selectively switching on individual electric energy consumers.
Furthermore, this apparatus also does not allow several or all the electric energy consumers under control to be energized simultaneously.
In addition, the apparatus in question is not provided with a means to protect the electric circuits under control in the case of voltage collapse in the supply circuit of the electric energy source.
Using this apparatus requires auxiliary switching elements.
For the above reasons the prior art apparatus when used to control a group of electric energy consumers does not allow the number of relays and supplementary switching elements to be appreciably reduced.
There is also known an electric circuit switching device (cf. USSR Application No. 2,195,531/07, 134,081, filed Dec. 1, 1975, U.S. Application No. 15,167, filed Feb. 26, 1979, FRG Application No. P.2904287 filed Feb. 5, 1979, Romanian Application Ser. No. 17,086/96,538 filed Feb. 7, 1979, French Application Ser. No. 7,903,871 filed Feb. 15, 1979, British Application Ser. No. 7,904,820 filed Feb. 12, 1979, Indian Application Ser. No. 103/Cal/79 filed Jan. 31, 1979/which comprises main contacts composed of stationary contact members located in circle on an insulating panel, and a movable contact members, auxiliary contacts for switching local control circuits of the apparatus, means for selectively operating contacts, provided with contact position fixing devices. The device further includes a contactor having at least one projection to actuate the contact closing means, a rotational electromechanical drive having a shaft passing through the central aperture in said insulating panel and being adapted to rotate the contactor through a predetermined angle. The device also includes an electromagnetic drive incorporating an electromagnet for closing contacts, which electromagnet is provided with a hollow armature enveloping the shaft of the electromechanical drive, with the said contactor being mounted on the said hollow armature. The said electromagnet is also adapted to move the said contactor along the shaft of the electromechanical drive while closing contacts. The electromagnetic drive is also provided with electromagnets to open contacts, one of which electromagnets is constructed similar to the electromagnet for making contacts and is adapted to actuate the contact breaker, while the other one operates in the case of voltage collapse in the supply circuit of the electric energy consumer to break all the contacts and to thereby provide a zero-voltage protection.
The above device makes it possible with the aid of only one common drive for making contacts in the circuit under control to selectively connect a group of power supply electric circuits so as to allow several or all the circuits of said group to be energized simultaneously. Such construction of the above device permits the number of elements required for switching said group of circuits to be appreciably reduced. Thus, for instance, the number of electromagnets involved is reduced by half. In addition, the presence of the unit adapted for setting an angle of rotation of a contact maker and contact breaker and provided with additional contacts allows checking insulation of all the circuits under control before making them with the use of only one relay.
However, when incorporated in the systems operating in explosion-hazardous places, the advantages of this device cannot be utilized to the best.
Thus, for instance, the presence of separate disconnecting electromagnet and electromagnet for zero-voltage protection complicates the construction of the device and the manufacture thereof. Furthermore, it does not provide for a rapid selective disconnection of the circuits under control, since such operation takes a certain time for finding the required contact corresponding to a circuit to be disconnected.
A still further advantage of the above device is that it is not protected against collapse of control which may happen as a result of, for example, failure of the electromagnet for breaking contacts, which results in that the circuits under control cannot be selectively disconnected.